- Email: [email protected]
Difficult-to-treat Gram-negative bone and joint infections: efficacy and safety of prolonged intravenous colistin
International Journal of Antimicrobial Agents 41 (2013) 197–202
Contents lists available at SciVerse ScienceDirect
International Journal of Antimicrobial Agents journal homepage: http://www.elsevier.com/locate/ijantimicag
Letters to the Editor
Difficult-to-treat Gram-negative bone and joint infections: efficacy and safety of prolonged intravenous colistin夽 Sir, Neglected in the 1980s because of a high incidence of nephrotoxicity, colistin (COL) has recently re-emerged as a last-line antimicrobial to face the emergence of multidrug-resistant (MDR) Gram-negative rods [1]. Although the manufacturer recommends a dosage of 50 000 IU/kg/day, the optimum dose, safety and efficacy of prolonged use of COL in patients with bone and joint infections (BJIs) are unknown. We addressed these questions in a multicentre (eight centres in France and one centre in Switzerland), retrospective, cohort study from 2006 to 2011 involving patients aged ≥18 years with BJIs receiving intravenous (i.v.) COL initially prescribed for ≥21 days. MDR and extensively drug-resistant (XDR) were defined as previously described [2]. Nineteen patients were included (13 males) with a median age of 54.4 years [interquartile range (IQR) 31.8–69.3 years] and a median Charlson co-morbidity index of 2 (IQR 0–3.5). Two patients had pre-existing renal failure. There were 14 cases of osteomyelitis (73.7%) and 5 joint infections (26.3%); 12 cases (63.2%) were associated with orthopaedic implants and 15 (78.9%) were chronic (i.e. persisting for >4 weeks). Fistulae and abscesses were present in 13 (68.4%) and 9 (47.4%) cases, respectively. The causative pathogens were Pseudomonas aeruginosa and Enterobacter spp. in 16 patients (84.2%) and 3 patients (15.8%), respectively. Four cases (21.1%) were MDR and 13 (68.4%) were XDR. All were susceptible to COL. Ten infections (52.6%) were polymicrobial. Colistin was used as a second-line regimen in 17 patients (89.5%). Surgical treatment was always performed (orthopaedic implants were removed in all but one case). The median COL dose was 50 000 IU/kg/day (IQR 40 700–55 800 IU/kg/day), administered in two (n = 9; 47.4%) or three (n = 7; 36.8%) i.v. injections or by continuous infusion (n = 3; 15.8%). The median duration of COL therapy was 81 days (IQR 37.0–148.5 days). Nine patients (47.4%) received concomitant i.v. hydration. The median follow-up after discontinuation of COL was 27.7 weeks (IQR 5.1–59.3 weeks). Remission was achieved in 14 cases (73.7%). Three patients (15.8%) experienced persistent/recurrent infection. One patient had to be amputated. One patient died from osteomyelitis complication. All patients with unfavourable outcome had chronic orthopaedic device-associated BJIs, leading to a treatment failure rate of 41.7% in this subgroup despite
夽 This work was presented as a slide presentation at the 51st Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC), 17–20 September 2011, Chicago, IL.
implant removal. Eight bacteriological samples during treatment were available, of which seven (87.5%) were sterile. In one patient with persistent infection receiving low doses of colistin (36 000 IU/kg/day), the bacteriological sample at the time of amputation yielded a colistin-resistant Enterobacter aerogenes (minimum inhibitory concentration = 16 mg/L). No patient developed a serious adverse event (CTCAE v.4.03 classification; http://evs.nci.nih.gov/). Eight patients (42.1%) developed grade 1–2 adverse events attributed to COL. Four patients (21.1%) experienced grade 1 acute renal failure that led to treatment discontinuation in one patient at Day 10. One other patient received high doses of colistin (240 000 IU/kg/day) leading to creatinine elevation 3× above baseline (grade 2) and colistin discontinuation at Day 33. The median delay in the occurrence of acute renal failure was 20 days (IQR 17–93 days). Regarding the 18 patients who received <75 000 IU/kg/day of COL, the baseline serum creatinine value significantly increased during COL therapy (Fig. 1) (P = 0.001, Mann–Whitney U-test), with a trend toward a lower maximum creatinine level in patients receiving i.v. hydration. No factor was significantly associated with renal failure. The creatinine level returned to baseline after discontinuation of COL in all patients. Two eosinophil blood count elevations (<2 g/L) occurred, leading to treatment interruption in one patient at Day 140. Finally, a transient distal dysesthesia was observed in one patient. To date, COL has not been considered as an alternative therapy in BJIs because (i) there are no reliable studies on the bone distribution of COL and (ii) long-term use of a nephrotoxic antimicrobial is often avoided. In the literature, we have identified approximately 30 cases of BJIs treated by 2–15 million IU/day of COL for ca. 6 weeks, ranging from a few days to 24 weeks, without treatment failure. The current results fit with recent reports mentioning nephrotoxicity rates of 10–30%, being reversible in ca. 90% of cases [3]. Nephrotoxicity risk factors include a colistin dosage ≥75 000 IU/kg/day, age, pre-existing renal insufficiency, hypoalbuminaemia and the administration of other nephrotoxins [1,4]. Particular attention should be paid to orthopaedic device infections for which the treatment failure rate was 42% in this report. In such situations, higher doses of COL might be useful against P. aeruginosa strains forming biofilms, one of the leading virulence factors associated with relapse [5]. Finally, it would be interesting to evaluate the clinical effectiveness of in vitro synergistic antibiotic combinations containing COL and rifampicin, which could also be effective in preventing the development of COL resistance. In conclusion, a ‘conventional’ dose of 50 000 IU/kg/day of prolonged i.v. COL provides a satisfactory cure rate of MDR/XDR Gram-negative BJIs, with an acceptable tolerance in patients with normal renal function. In the case of implant-associated infection, the dose might be elevated to 75 000 IU/kg/day using concomitant i.v. hydration and avoiding other nephrotoxins. Further studies are needed to confirm these results.
0924-8579/$ – see front matter. Published by Elsevier B.V. on behalf of International Society of Chemotherapy.
198
Letters to the Editor / International Journal of Antimicrobial Agents 41 (2013) 197–202
Fig. 1. Evolution of creatinine plasma levels during colistin therapy. NS, not significant.
Acknowledgments
Florent Valour a,b,∗ Service des maladies infectieuses et tropicales, Hospices Civils de Lyon, Université Claude Bernard Lyon 1, Lyon, France b INSERM U851, Pathogénie bactérienne et immunité innée, Lyon, France
a
BJIs Study Group: Florent Valour, Tristan Ferry, Thomas Perpoint, Florence Ader, Marie-Paule Vallat, Franc¸ois Biron, André Boibieux, Christian Chidiac, Dominique Peyramond, Frédéric Laurent (Lyon); Hervé Dutronc, Michel Dupon (Bordeaux); Aurélien Dinh, Anne-Claude Cremieux (Garches); Sonia Baumard, Christophe Strady (Reims), Patricia Pavèse (Grenoble); Olivier Lesens (Clermont-Ferrand); Emmanuel Forestier (Chambéry); Ilker Uckay (Genève); and Frédéric Lucht, Céline Cazorla (St Etienne). Funding: No funding sources. Competing interests: None declared. Ethical approval: Not required.
References [1] Yahav D, Farbman L, Leibovici L, Paul M. Colistin: new lessons on an old antibiotic. Clin Microbiol Infect 2012;18:18–29. [2] Magiorakos AP, Srinivasan A, Carey RB, Carmeli Y, Falagas ME, Giske CG, et al. Multidrug-resistant, extensively drug-resistant and pandrug-resistant bacteria: an international expert proposal for interim standard definitions for acquired resistance. Clin Microbiol Infect 2012;18:268–81. [3] Falagas ME, Kasiakou SK. Toxicity of polymyxins: a systematic review of the evidence from old and recent studies. Crit Care 2006;10:R27. [4] Pogue JM, Lee J, Marchaim D, Yee V, Zhao JJ, Chopra T, et al. Incidence of and risk factors for colistin-associated nephrotoxicity in a large academic health system. Clin Infect Dis 2011;53:879–84. [5] Hengzhuang W, Wu H, Ciofu O, Song Z, Hoiby N. Pharmacokinetics/pharmacodynamics of colistin and imipenem on mucoid and nonmucoid Pseudomonas aeruginosa biofilms. Antimicrob Agents Chemother 2011;55: 4469–74.
Hervé Dutronc Service des maladies infectieuses et tropicales, Hôpital Pellegrin, Université Victor Segalen Bordeaux 2, Bordeaux, France Aurélien Dinh Département de médecine aiguë spécialisée, Hôpital Raymond Poincaré, Assistance Publique–Hôpitaux de Paris, Université Versailles Saint-Quentin, Garches, France Céline Cazorla Service des maladies infectieuses et tropicales, Centre hospitalo-universitaire de St Etienne, Université de St Etienne, France Patricia Pavèse Service des maladies infectieuses et tropicales, Centre hospitalo-universitaire de Grenoble, France Olivier Lesens Service des maladies infectieuses et tropicales, Centre hospitalo-universitaire de Clermont-Ferrand, France Ilker Uc¸kay Service des maladies infectieuses, Hôpitaux Universitaires de Genève, Switzerland
Letters to the Editor / International Journal of Antimicrobial Agents 41 (2013) 197–202
Christian Chidiac c,d Tristan Ferry c,d , for the Colistin BJIs Study Group c Service des maladies infectieuses et tropicales, Hospices Civils de Lyon, Université Claude Bernard Lyon 1, Lyon, France d INSERM U851, Pathogénie bactérienne et immunité innée, Lyon, France ∗ Corresponding author. Present address: Infectious Diseases Department, Hospices Civils de Lyon, Hôpital de la Croix-Rousse, 103 Grande-Rue de la Croix-Rousse, 69317 Lyon cedex 04, France. Tel.: +33 4 72 07 11 07; fax: +33 4 72 07 17 50. E-mail address: fl[email protected] (F. Valour)
14 July 2012 doi:10.1016/j.ijantimicag.2012.09.016
Investigation of biofilm formation in Acinetobacter baumannii isolates and their colistin susceptibilities in biofilm Sir, Acinetobacter baumannii has gained importance as it causes serious infections and its incidence has increased. Thus, studies were conducted on the ability and mechanism of biofilm formation in A. baumannii. The ability of A. baumannii to form biofilm is an important virulence factor since biofilm enables long-term survival in the hospital environment and provides resistance to antimicrobials during treatment of infection [1]. Treatment of infections has become more difficult owing to increased resistance rates of microorganisms and this has resulted in the use of old antibiotics such as colistin [2]. The aim of the current study was to determine the rate of biofilm formation by isolates of A. baumannii isolated from patients who were hospitalised during a 6-month period and to determine the effects of colistin (polymyxin E), which is the only option for treatment of multidrug-resistant isolates, on biofilm formation and bacteria residing in the biofilm. In total, 152 A. baumannii isolates were included in the study. Sensitivity to colistin was determined by the standard broth microdilution method. The qualitative tube method was used to determine biofilm formation, and the spectrometric microtitration plate method was used for quantitation [3]. Based on the amount of biofilm formed by A. baumannii ATCC 19606, in total 77 A. baumannii isolates were tested to investigate the effect of colistin on the formed biofilm layer. Biofilm inhibitory concentrations (BICs) were determined as described previously [4]. Kappa test and Wilcoxon matched-pairs test were used to analyse the study data, and a P-value of <0.05 was considered statistically significant. When data obtained from biofilm sensitivity tests were analysed by Wilcoxon matched-pairs test, there was no statistically significant difference between the optical density (OD) measured before antibiotic treatment and the OD measured after antibiotic treatment (P > 0.05). However, a decrease was found in the OD in 33 of the 77 clinical isolates studied at high concentrations (64–32 g/mL). In the current study, all isolates were sensitive to colistin and minimum inhibitory concentrations (MICs) ranged between 0.125 g/mL and 1 g/mL. In biofilm tests, biofilm formation was negative in 83 (54.6%) of the 152 A. baumannii isolates by the tube method, whilst biofilm formation was positive in 69 isolates (45.4%). In the microtitration plate method, biofilm formation was negative in 75 isolates (49.3%), moderate in 68 isolates (44.7%) and strong in 9 isolates (5.9%). Absorbance was measured using the microtitration plate method and biofilm formation was positive in only 8 of the 83 biofilm-negative isolates by the tube method. Agreement between the microtitration plate method used for
199
determining biofilm formation and the tube method was 89.5% and this agreement level was statistically significant (P < 0.001). Colistin MICs of isolates were in the range of 0.125 g/mL and 1 g/mL, and the MIC50 value (MIC for 50% of the isolates) of colistin was 0.25 g/mL, whereas the MIC90 value (MIC for 90% of the isolates) was calculated as 1 g/mL. BICs were determined at far higher concentrations compared with MIC values. BIC values ranged between 32 g/mL and 4096 g/mL, and the BIC50 value was 128 g/mL, whereas the BIC90 value was calculated as 512 g/mL; accordingly, the lowest BIC value of isolates for colistin was 32-fold the MIC90 value. BIC90 values were found to be 512-fold the MIC90 value. Biofilm formation significantly reduces antibiotic sensitivity according to some of the studies published in the literature determining the effects of many different antibiotics on biofilm produced by various bacteria. There are different studies investigating the in vivo relationship between biofilm and antibacterial agents. In studies comparing MIC and BIC values, BIC and MIC values were close for some antibiotics, whilst BIC values of some bacteria were several times the MIC value [5]. In conclusion, biofilm formation in A. baumannii isolates may be influenced by many factors. This diversity demonstrates that a particular isolate may exert different biofilm formation tendencies under different conditions. Much higher BIC values in comparison with MIC values, as indicated by various studies, indicate that antimicrobial therapy of biofilm-forming bacteria is more challenging. This ability will make treatment of infections more difficult and this fact should be taken into consideration when treatment protocols are established. When the high biofilm production potential of A. baumannii is considered, it should be remembered that therapeutic activity may vary when treatment with colistin is planned for infections caused by this bacteria. In light of abovementioned data, further studies are required in order to demonstrate how biofilm production by A. baumannii isolates is influenced by different antibiotics. Moreover, further molecular, genotypic and phenotypic studies are required in order to prevent biofilm formation. Funding: This study was supported by Ondokuz Mayis University (Samsun, Turkey) (project no: PYO.TIP.1904.10.017). Competing interests: None declared. Ethical approval: Not required. References [1] Tomaras AP, Dorsey CW, Edelman RE, Actis LA. Attachment to and biofilm formation on abiotic surfaces by Acinetobacter baumannii: involvement of a novel chaperone-usher pili assembly system. Microbiology 2003;149:3473–84. [2] Saltoglu N. Acinetobacter baumannii enfeksiyonları ve tedavisi. In: XIII Turk KLIMIK Kongresi [Turkish KLIMIK Congress]. 2007. p. 204–7. [3] Christensen GD, Simpson WA, Younger JJ, Baddour LM, Barrett FF, Melton DM, et al. Adherence of coagulase-negative staphylococci to plastic tissue culture plates: a quantitative model for the adherence of staphylococci to medical devices. J Clin Microbiol 1985;22:996–1006. [4] Tré-Hardy M, Vanderbist F, Traore H, Devleeschouver MJ. In vitro activity of antibiotic combinations against Pseudomonas aeruginosa biofilm and planktonic cultures. Int J Antimicrob Agents 2008;31:329–36. [5] Moskowitz SM, Foster JM, Emerson J, Burns JL. Clinically feasible biofilm susceptibility assay for isolates of Pseudomonas aeruginosa from patients with cystic fibrosis. J Clin Microbiol 2004;42:1915–22.
Fikriye Milletli Sezgin Ahmet Yilmaz Coban ∗ Murat Gunaydin Ondokuz Mayis University, Medical School, Department of Medical Microbiology, 55139 Samsun, Turkey ∗ Corresponding
author. Tel.: +90 362 312 1919/3526; fax: +90 362 457 6041. E-mail address: [email protected] (A.Y. Coban) 26 June 2012
doi:10.1016/j.ijantimicag.2012.10.003
Contents lists available at SciVerse ScienceDirect
International Journal of Antimicrobial Agents journal homepage: http://www.elsevier.com/locate/ijantimicag
Letters to the Editor
Difficult-to-treat Gram-negative bone and joint infections: efficacy and safety of prolonged intravenous colistin夽 Sir, Neglected in the 1980s because of a high incidence of nephrotoxicity, colistin (COL) has recently re-emerged as a last-line antimicrobial to face the emergence of multidrug-resistant (MDR) Gram-negative rods [1]. Although the manufacturer recommends a dosage of 50 000 IU/kg/day, the optimum dose, safety and efficacy of prolonged use of COL in patients with bone and joint infections (BJIs) are unknown. We addressed these questions in a multicentre (eight centres in France and one centre in Switzerland), retrospective, cohort study from 2006 to 2011 involving patients aged ≥18 years with BJIs receiving intravenous (i.v.) COL initially prescribed for ≥21 days. MDR and extensively drug-resistant (XDR) were defined as previously described [2]. Nineteen patients were included (13 males) with a median age of 54.4 years [interquartile range (IQR) 31.8–69.3 years] and a median Charlson co-morbidity index of 2 (IQR 0–3.5). Two patients had pre-existing renal failure. There were 14 cases of osteomyelitis (73.7%) and 5 joint infections (26.3%); 12 cases (63.2%) were associated with orthopaedic implants and 15 (78.9%) were chronic (i.e. persisting for >4 weeks). Fistulae and abscesses were present in 13 (68.4%) and 9 (47.4%) cases, respectively. The causative pathogens were Pseudomonas aeruginosa and Enterobacter spp. in 16 patients (84.2%) and 3 patients (15.8%), respectively. Four cases (21.1%) were MDR and 13 (68.4%) were XDR. All were susceptible to COL. Ten infections (52.6%) were polymicrobial. Colistin was used as a second-line regimen in 17 patients (89.5%). Surgical treatment was always performed (orthopaedic implants were removed in all but one case). The median COL dose was 50 000 IU/kg/day (IQR 40 700–55 800 IU/kg/day), administered in two (n = 9; 47.4%) or three (n = 7; 36.8%) i.v. injections or by continuous infusion (n = 3; 15.8%). The median duration of COL therapy was 81 days (IQR 37.0–148.5 days). Nine patients (47.4%) received concomitant i.v. hydration. The median follow-up after discontinuation of COL was 27.7 weeks (IQR 5.1–59.3 weeks). Remission was achieved in 14 cases (73.7%). Three patients (15.8%) experienced persistent/recurrent infection. One patient had to be amputated. One patient died from osteomyelitis complication. All patients with unfavourable outcome had chronic orthopaedic device-associated BJIs, leading to a treatment failure rate of 41.7% in this subgroup despite
夽 This work was presented as a slide presentation at the 51st Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC), 17–20 September 2011, Chicago, IL.
implant removal. Eight bacteriological samples during treatment were available, of which seven (87.5%) were sterile. In one patient with persistent infection receiving low doses of colistin (36 000 IU/kg/day), the bacteriological sample at the time of amputation yielded a colistin-resistant Enterobacter aerogenes (minimum inhibitory concentration = 16 mg/L). No patient developed a serious adverse event (CTCAE v.4.03 classification; http://evs.nci.nih.gov/). Eight patients (42.1%) developed grade 1–2 adverse events attributed to COL. Four patients (21.1%) experienced grade 1 acute renal failure that led to treatment discontinuation in one patient at Day 10. One other patient received high doses of colistin (240 000 IU/kg/day) leading to creatinine elevation 3× above baseline (grade 2) and colistin discontinuation at Day 33. The median delay in the occurrence of acute renal failure was 20 days (IQR 17–93 days). Regarding the 18 patients who received <75 000 IU/kg/day of COL, the baseline serum creatinine value significantly increased during COL therapy (Fig. 1) (P = 0.001, Mann–Whitney U-test), with a trend toward a lower maximum creatinine level in patients receiving i.v. hydration. No factor was significantly associated with renal failure. The creatinine level returned to baseline after discontinuation of COL in all patients. Two eosinophil blood count elevations (<2 g/L) occurred, leading to treatment interruption in one patient at Day 140. Finally, a transient distal dysesthesia was observed in one patient. To date, COL has not been considered as an alternative therapy in BJIs because (i) there are no reliable studies on the bone distribution of COL and (ii) long-term use of a nephrotoxic antimicrobial is often avoided. In the literature, we have identified approximately 30 cases of BJIs treated by 2–15 million IU/day of COL for ca. 6 weeks, ranging from a few days to 24 weeks, without treatment failure. The current results fit with recent reports mentioning nephrotoxicity rates of 10–30%, being reversible in ca. 90% of cases [3]. Nephrotoxicity risk factors include a colistin dosage ≥75 000 IU/kg/day, age, pre-existing renal insufficiency, hypoalbuminaemia and the administration of other nephrotoxins [1,4]. Particular attention should be paid to orthopaedic device infections for which the treatment failure rate was 42% in this report. In such situations, higher doses of COL might be useful against P. aeruginosa strains forming biofilms, one of the leading virulence factors associated with relapse [5]. Finally, it would be interesting to evaluate the clinical effectiveness of in vitro synergistic antibiotic combinations containing COL and rifampicin, which could also be effective in preventing the development of COL resistance. In conclusion, a ‘conventional’ dose of 50 000 IU/kg/day of prolonged i.v. COL provides a satisfactory cure rate of MDR/XDR Gram-negative BJIs, with an acceptable tolerance in patients with normal renal function. In the case of implant-associated infection, the dose might be elevated to 75 000 IU/kg/day using concomitant i.v. hydration and avoiding other nephrotoxins. Further studies are needed to confirm these results.
0924-8579/$ – see front matter. Published by Elsevier B.V. on behalf of International Society of Chemotherapy.
198
Letters to the Editor / International Journal of Antimicrobial Agents 41 (2013) 197–202
Fig. 1. Evolution of creatinine plasma levels during colistin therapy. NS, not significant.
Acknowledgments
Florent Valour a,b,∗ Service des maladies infectieuses et tropicales, Hospices Civils de Lyon, Université Claude Bernard Lyon 1, Lyon, France b INSERM U851, Pathogénie bactérienne et immunité innée, Lyon, France
a
BJIs Study Group: Florent Valour, Tristan Ferry, Thomas Perpoint, Florence Ader, Marie-Paule Vallat, Franc¸ois Biron, André Boibieux, Christian Chidiac, Dominique Peyramond, Frédéric Laurent (Lyon); Hervé Dutronc, Michel Dupon (Bordeaux); Aurélien Dinh, Anne-Claude Cremieux (Garches); Sonia Baumard, Christophe Strady (Reims), Patricia Pavèse (Grenoble); Olivier Lesens (Clermont-Ferrand); Emmanuel Forestier (Chambéry); Ilker Uckay (Genève); and Frédéric Lucht, Céline Cazorla (St Etienne). Funding: No funding sources. Competing interests: None declared. Ethical approval: Not required.
References [1] Yahav D, Farbman L, Leibovici L, Paul M. Colistin: new lessons on an old antibiotic. Clin Microbiol Infect 2012;18:18–29. [2] Magiorakos AP, Srinivasan A, Carey RB, Carmeli Y, Falagas ME, Giske CG, et al. Multidrug-resistant, extensively drug-resistant and pandrug-resistant bacteria: an international expert proposal for interim standard definitions for acquired resistance. Clin Microbiol Infect 2012;18:268–81. [3] Falagas ME, Kasiakou SK. Toxicity of polymyxins: a systematic review of the evidence from old and recent studies. Crit Care 2006;10:R27. [4] Pogue JM, Lee J, Marchaim D, Yee V, Zhao JJ, Chopra T, et al. Incidence of and risk factors for colistin-associated nephrotoxicity in a large academic health system. Clin Infect Dis 2011;53:879–84. [5] Hengzhuang W, Wu H, Ciofu O, Song Z, Hoiby N. Pharmacokinetics/pharmacodynamics of colistin and imipenem on mucoid and nonmucoid Pseudomonas aeruginosa biofilms. Antimicrob Agents Chemother 2011;55: 4469–74.
Hervé Dutronc Service des maladies infectieuses et tropicales, Hôpital Pellegrin, Université Victor Segalen Bordeaux 2, Bordeaux, France Aurélien Dinh Département de médecine aiguë spécialisée, Hôpital Raymond Poincaré, Assistance Publique–Hôpitaux de Paris, Université Versailles Saint-Quentin, Garches, France Céline Cazorla Service des maladies infectieuses et tropicales, Centre hospitalo-universitaire de St Etienne, Université de St Etienne, France Patricia Pavèse Service des maladies infectieuses et tropicales, Centre hospitalo-universitaire de Grenoble, France Olivier Lesens Service des maladies infectieuses et tropicales, Centre hospitalo-universitaire de Clermont-Ferrand, France Ilker Uc¸kay Service des maladies infectieuses, Hôpitaux Universitaires de Genève, Switzerland
Letters to the Editor / International Journal of Antimicrobial Agents 41 (2013) 197–202
Christian Chidiac c,d Tristan Ferry c,d , for the Colistin BJIs Study Group c Service des maladies infectieuses et tropicales, Hospices Civils de Lyon, Université Claude Bernard Lyon 1, Lyon, France d INSERM U851, Pathogénie bactérienne et immunité innée, Lyon, France ∗ Corresponding author. Present address: Infectious Diseases Department, Hospices Civils de Lyon, Hôpital de la Croix-Rousse, 103 Grande-Rue de la Croix-Rousse, 69317 Lyon cedex 04, France. Tel.: +33 4 72 07 11 07; fax: +33 4 72 07 17 50. E-mail address: fl[email protected] (F. Valour)
14 July 2012 doi:10.1016/j.ijantimicag.2012.09.016
Investigation of biofilm formation in Acinetobacter baumannii isolates and their colistin susceptibilities in biofilm Sir, Acinetobacter baumannii has gained importance as it causes serious infections and its incidence has increased. Thus, studies were conducted on the ability and mechanism of biofilm formation in A. baumannii. The ability of A. baumannii to form biofilm is an important virulence factor since biofilm enables long-term survival in the hospital environment and provides resistance to antimicrobials during treatment of infection [1]. Treatment of infections has become more difficult owing to increased resistance rates of microorganisms and this has resulted in the use of old antibiotics such as colistin [2]. The aim of the current study was to determine the rate of biofilm formation by isolates of A. baumannii isolated from patients who were hospitalised during a 6-month period and to determine the effects of colistin (polymyxin E), which is the only option for treatment of multidrug-resistant isolates, on biofilm formation and bacteria residing in the biofilm. In total, 152 A. baumannii isolates were included in the study. Sensitivity to colistin was determined by the standard broth microdilution method. The qualitative tube method was used to determine biofilm formation, and the spectrometric microtitration plate method was used for quantitation [3]. Based on the amount of biofilm formed by A. baumannii ATCC 19606, in total 77 A. baumannii isolates were tested to investigate the effect of colistin on the formed biofilm layer. Biofilm inhibitory concentrations (BICs) were determined as described previously [4]. Kappa test and Wilcoxon matched-pairs test were used to analyse the study data, and a P-value of <0.05 was considered statistically significant. When data obtained from biofilm sensitivity tests were analysed by Wilcoxon matched-pairs test, there was no statistically significant difference between the optical density (OD) measured before antibiotic treatment and the OD measured after antibiotic treatment (P > 0.05). However, a decrease was found in the OD in 33 of the 77 clinical isolates studied at high concentrations (64–32 g/mL). In the current study, all isolates were sensitive to colistin and minimum inhibitory concentrations (MICs) ranged between 0.125 g/mL and 1 g/mL. In biofilm tests, biofilm formation was negative in 83 (54.6%) of the 152 A. baumannii isolates by the tube method, whilst biofilm formation was positive in 69 isolates (45.4%). In the microtitration plate method, biofilm formation was negative in 75 isolates (49.3%), moderate in 68 isolates (44.7%) and strong in 9 isolates (5.9%). Absorbance was measured using the microtitration plate method and biofilm formation was positive in only 8 of the 83 biofilm-negative isolates by the tube method. Agreement between the microtitration plate method used for
199
determining biofilm formation and the tube method was 89.5% and this agreement level was statistically significant (P < 0.001). Colistin MICs of isolates were in the range of 0.125 g/mL and 1 g/mL, and the MIC50 value (MIC for 50% of the isolates) of colistin was 0.25 g/mL, whereas the MIC90 value (MIC for 90% of the isolates) was calculated as 1 g/mL. BICs were determined at far higher concentrations compared with MIC values. BIC values ranged between 32 g/mL and 4096 g/mL, and the BIC50 value was 128 g/mL, whereas the BIC90 value was calculated as 512 g/mL; accordingly, the lowest BIC value of isolates for colistin was 32-fold the MIC90 value. BIC90 values were found to be 512-fold the MIC90 value. Biofilm formation significantly reduces antibiotic sensitivity according to some of the studies published in the literature determining the effects of many different antibiotics on biofilm produced by various bacteria. There are different studies investigating the in vivo relationship between biofilm and antibacterial agents. In studies comparing MIC and BIC values, BIC and MIC values were close for some antibiotics, whilst BIC values of some bacteria were several times the MIC value [5]. In conclusion, biofilm formation in A. baumannii isolates may be influenced by many factors. This diversity demonstrates that a particular isolate may exert different biofilm formation tendencies under different conditions. Much higher BIC values in comparison with MIC values, as indicated by various studies, indicate that antimicrobial therapy of biofilm-forming bacteria is more challenging. This ability will make treatment of infections more difficult and this fact should be taken into consideration when treatment protocols are established. When the high biofilm production potential of A. baumannii is considered, it should be remembered that therapeutic activity may vary when treatment with colistin is planned for infections caused by this bacteria. In light of abovementioned data, further studies are required in order to demonstrate how biofilm production by A. baumannii isolates is influenced by different antibiotics. Moreover, further molecular, genotypic and phenotypic studies are required in order to prevent biofilm formation. Funding: This study was supported by Ondokuz Mayis University (Samsun, Turkey) (project no: PYO.TIP.1904.10.017). Competing interests: None declared. Ethical approval: Not required. References [1] Tomaras AP, Dorsey CW, Edelman RE, Actis LA. Attachment to and biofilm formation on abiotic surfaces by Acinetobacter baumannii: involvement of a novel chaperone-usher pili assembly system. Microbiology 2003;149:3473–84. [2] Saltoglu N. Acinetobacter baumannii enfeksiyonları ve tedavisi. In: XIII Turk KLIMIK Kongresi [Turkish KLIMIK Congress]. 2007. p. 204–7. [3] Christensen GD, Simpson WA, Younger JJ, Baddour LM, Barrett FF, Melton DM, et al. Adherence of coagulase-negative staphylococci to plastic tissue culture plates: a quantitative model for the adherence of staphylococci to medical devices. J Clin Microbiol 1985;22:996–1006. [4] Tré-Hardy M, Vanderbist F, Traore H, Devleeschouver MJ. In vitro activity of antibiotic combinations against Pseudomonas aeruginosa biofilm and planktonic cultures. Int J Antimicrob Agents 2008;31:329–36. [5] Moskowitz SM, Foster JM, Emerson J, Burns JL. Clinically feasible biofilm susceptibility assay for isolates of Pseudomonas aeruginosa from patients with cystic fibrosis. J Clin Microbiol 2004;42:1915–22.
Fikriye Milletli Sezgin Ahmet Yilmaz Coban ∗ Murat Gunaydin Ondokuz Mayis University, Medical School, Department of Medical Microbiology, 55139 Samsun, Turkey ∗ Corresponding
author. Tel.: +90 362 312 1919/3526; fax: +90 362 457 6041. E-mail address: [email protected] (A.Y. Coban) 26 June 2012
doi:10.1016/j.ijantimicag.2012.10.003